Featured Research

Key factor in early auditory system development discovered

Date:

May 20, 2014

Source:

NIH/National Institute on Deafness and Other Communication Disorders

Summary:

A molecule in an animal model that acts as a key player in establishing the organization of the auditory system has been discovered in a recent study. The molecule, a protein known as Bmp7, is produced during embryonic development and acts to help sensory cells find their ultimate position on the tonotopic map, which is the fundamental principle of organization in the auditory system.

Share This

Researchers at the National Institutes of Health have uncovered a molecule in an animal model that acts as a key player in establishing the organization of the auditory system. The molecule, a protein known as Bmp7, is produced during embryonic development and acts to help sensory cells find their ultimate position on the tonotopic map, which is the fundamental principle of organization in the auditory system. The tonotopic map groups sensory cells by the sound frequencies that stimulate them. The study is the first to identify one of the molecular mechanisms that determines position.

Related Articles

Findings from the study, led by Zoe F. Mann, Ph.D and Matthew W. Kelley, Ph.D., of the Laboratory of Cochlear Development at the National Institute on Deafness and Other Communication Disorders (NIDCD), were published in the May 20, 2014 issue of Nature Communications. The research was performed in collaboration with scientists from the University of Virginia (UVa) School of Medicine, Charlottesville, and Imperial College in London. The American Hearing Research Foundation provided additional support.

An additional study, appearing in the same edition, is led by NIDCD-supported researchers Benjamin R. Thiede, Ph.D., and Jeffrey T. Corwin, Ph.D. at UVa. Working in collaboration with Drs. Mann and Kelley, the researchers reveal that another signaling molecule, retinoic acid, acts in concert with Bmp7 to position cells.

"The findings could open doors to therapies that take advantage of Bmp7's navigational talents to direct the formation of regenerated sensory cells that are tuned to respond to a specific frequency," says James F. Battey, Jr., M.D., Ph.D., director of NIDCD. "Since many forms of hearing loss are limited to specific frequencies, this approach could lead to replacement sensory cells that are tailored to individual needs."

The human ear can detect a wide range of frequencies, from the low rumble of distant thunder to the high-pitched whine of a mosquito. The sensory cells that detect these sounds are called hair cells, named for the hair-like strands that cluster on their tops. Hair cells are spread across a flat surface called the basilar membrane, which rolls up like a carpet and tucks into a snail shell-shaped structure in the inner ear called the cochlea.

Part of what accounts for our remarkable range of hearing is that hair cells have different specializations. Rather than working to sense all audible frequencies, each of our roughly 16,000 hair cells is dedicated to a narrow range. Hair cells are ordered along the basilar membrane's length, or axis, according to the frequency they detect. Those that sense low pitches are at one end and those that detect high-frequency sounds are at the opposite end. The cells in between step through the mid-range pitches.

This spatial arrangement of hair cells on the basilar membrane-the tonotopic map -- has been known for years. What hasn't been known is how each hair cell learns to "hear" specific frequencies.

"During development, hair cells at each position along the axis need to figure out where they are so that they know what frequency they should be listening to," said Dr. Kelley. "This is called positional identity. We wanted to know how hair cells figure out their position."

Dr. Kelley suspected that, like numbers on a ruler, the positions of hair cells along the basilar membrane were marked by stepwise differences in the level of a signaling molecule that would determine position. Molecular concentration gradients of this sort have been shown to steer the positioning of other cell types in the body during development.

To see if such a signaling molecule might be involved in the structural organization of the cochlea, Dr. Mann examined the basilar papilla from six-day old chick embryos. The basilar papilla in chickens is similar to the cochlea in mammals, with hair cells arranged along the length of its basilar membrane in a similar fashion according to frequency. The researchers reasoned that if a molecular concentration gradient were involved in positioning hair cells, the molecule's level would be higher at one end of the basilar papilla than the other.

When they split the basilar papilla in half looking for molecules, one stood out because of the striking difference in its level between the two halves -- Bmp7 -- a signaling protein known to play a role in the development of bone and kidneys. Additional experiments revealed a gradual gradient in the level of Bmp7 across the length of the basilar papilla.

The researchers next showed that Bmp7 promotes the development of low-frequency-sensing hair cells. When they bathed developing basilar papillas in a solution containing Bmp7, they found that all the hair cells developed characteristics of low-frequency-sensing hair cells, even those at the high-frequency end.

These findings suggest that during embryonic development, high levels of Bmp7 at one end of the basilar papilla signal the formation of low-frequency-sensing hair cells. Decreasing levels of Bmp7 along the length of the basilar papilla map with a gradual change towards tuning to higher frequencies.

In future work, Dr. Kelley and his team aim to use a mouse model to understand the role of Bmp7 in specifying the positioning of hair cells in a mammalian organism. Bmp7 is known to be present in cells of the inner ear in mammals, suggesting a possible role for the molecule in tuning. The researchers hope to be able to outline its precise role in patterning parts of the auditory system.

"The entire auditory system is assembled according to individual frequencies," said Dr. Kelley. "Complex sounds like music or speech that consist of many different frequencies are split into individual frequencies in the ear, processed through separate channels, and then reassembled in the brain. By revealing the part played by Bmp7 in patterning hair cells in the inner ear, we may have uncovered a broader role for the molecule in the auditory system as a whole."

NIH/National Institute on Deafness and Other Communication Disorders. "Key factor in early auditory system development discovered." ScienceDaily. ScienceDaily, 20 May 2014. <www.sciencedaily.com/releases/2014/05/140520123438.htm>.

NIH/National Institute on Deafness and Other Communication Disorders. (2014, May 20). Key factor in early auditory system development discovered. ScienceDaily. Retrieved March 31, 2015 from www.sciencedaily.com/releases/2014/05/140520123438.htm

NIH/National Institute on Deafness and Other Communication Disorders. "Key factor in early auditory system development discovered." ScienceDaily. www.sciencedaily.com/releases/2014/05/140520123438.htm (accessed March 31, 2015).

Featured Research

Mar. 31, 2015  Researchers have illuminated an important distinction between mice and humans: how human livers heal. The difference centers on a protein called PPAR alpha which activates liver ... full story

Mar. 31, 2015  Researchers have recorded the first direct observations of the micro-scale mechanisms behind the ability of skin to resist tearing. The results could be applied to the improvement of artificial skin, ... full story

Mar. 31, 2015  Fewer than half of the physicians trained in the United States in 2013 received formal education or training on the subject of exercise, according to new research. "There are immense medical benefits ... full story

Mar. 31, 2015  Memory and as well as connections between brain cells were restored in mice with a model of Alzheimer's given an experimental cancer drug, researchers report. "With this treatment, cells under ... full story

Mar. 31, 2015  Increasing state alcohol taxes could prevent thousands of deaths a year from car crashes, say researchers, who found alcohol-related motor vehicle crashes decreased after taxes on beer, wine and ... full story

Mar. 31, 2015  Alcoholism takes a toll on every aspect of a person's life, including skin problems. Now, a new research report helps explain why this happens and what might be done to address it. "The clinical ... full story

Mar. 31, 2015  A new population of 'memory' immune cells has been discovered by scientists, throwing light on what the body does when it sees a microbe for the second time. This insight, and others like it, will ... full story

Mar. 31, 2015  Coronary heart disease and stroke, two of the leading causes of death in the United States, are diseases associated with heightened platelet reactivity. A new study in humans suggests an underlying ... full story

Mar. 31, 2015  A new study had researchers seeking answers to why the therapeutic benefit afforded by SSRIs was so limited in children and teenagers. If researchers can uncover the biological mechanisms preventing ... full story

Featured Videos

Solitair Device Aims to Takes Guesswork out of Sun Safety

Reuters - Innovations Video Online (Mar. 31, 2015)  The Solitair device aims to take the confusion out of how much sunlight we should expose our skin to. Small enough to be worn as a tie or hair clip, it monitors the user&apos;s sun exposure by taking into account their skin pigment, location and schedule. Matthew Stock reports.
Video provided by Reuters

Soda, Salt and Sugar: The Next Generation of Taxes

Washington Post (Mar. 30, 2015)  Denisa Livingston, a health advocate for the Dinι Community Advocacy Alliance, and the Post&apos;s Abby Phillip discuss efforts around the country to make unhealthy food choices hurt your wallet as much as your waistline.
Video provided by Washington Post

S. Leone in New Anti-Ebola Lockdown

AFP (Mar. 28, 2015)  Sierra Leone imposed a three-day nationwide lockdown Friday for the second time in six months in a bid to prevent a resurgence of the deadly Ebola virus. Duration: 01:17
Video provided by AFP

Related Stories

Feb. 3, 2015  Gene expression within neurons is critical for the formation of memories, but it's difficult to identify genes whose expression is altered by learning. Now researchers have successfully ... full story

Oct. 23, 2013  Imagine the brain's delight when experiencing the sounds of Beethoven's "Moonlight Sonata" while simultaneously taking in a light show produced by a visualizer. A new study did ... full story

Aug. 22, 2012  Scientists have found that the ability to hear is lessened when, as a result of injury, a region of the brain responsible for processing sounds receives both visual and auditory ... full story

Oct. 16, 2011  Auditory working memory and attention, for example the ability to hear and then remember instructions while completing a task, are a necessary part of musical ability. But musical ability is also ... full story

Oct. 18, 2010  Just as we visually map a room by spatially identifying the objects in it, we map our aural world based on the frequencies of sounds. The neurons within the brain's auditory cortex are organized ... full story

ScienceDaily features breaking news and videos about the latest discoveries in health, technology, the environment, and more -- from major news services and leading universities, scientific journals, and research organizations.